1. Field of the Invention
The present invention relates to an occupant detection apparatus, which detects the presence of an occupant on a vehicle seat.
2. Description of Relevant Art
As an example of these kinds of apparatus, the seat-weight measuring device, which detects the presence of an occupant by measuring a weight of a vehicle seat and which is disclosed in Japanese unexamined patent publication JP2000-258233, has been discovered.
FIG. 7 is an enlarged sectional view in which the relevant part of the seat-weight measuring device installed in a vehicle cabin is indicated. FIG. 8 is a exploded perspective view showing a floor carpet on a floor panel.
As shown in FIG. 7, a seat-weight measurement device 100 comprises a weight sensor 120 and a load absorption unit (a pin bracket 121 and a pin 122). The load absorption unit, which absorbs the creep or deflection due to the weight applied to the vehicle seat, is provided between the vehicle seat 110 and the weight sensor 120. The weight sensor 120, which converts the weight of the vehicle seat 110 into electrical signal, comprises a sensor plate 125 made of plate spring and a strain gauge 126 made of an insulating layer (not shown) formed by stacking electric circuits.
One end of the weight sensor 120 is fixed at a base 123 of a vehicle cabin, and the other end of the weight sensor 120 connects with a movable part (not shown) of the arm 124. Here, the arm 124 is pushed by a rail 130 of the vehicle seat 110 and is displaced, when a load applied to the vehicle seat 110 is transferred to the movable part.
In this seat-weight measurement device 100, when an occupant sits on the vehicle seat 110 and the vehicle seat 110 receives a weight of an occupant, a seat frame 111 is moved downwardly. In this occasion, since the pin bracket 121 and pin 122 are pushed by the seat frame 111 and are moved downwardly (a direction shown by arrow B), a bending moment due to the downward movement of the pin bracket 121 and pin 122 is detected by the weight sensor 120.
The seat-weight measurement device 100 measures the amount of the load applied to the vehicle seat 110 by processing electrical signal, which is obtained from the strain gauge 126 and is fluctuated in compliance with the bending moment.
The load absorption unit includes a pin bracket 121 and an arm 124. The pin bracket 121, which is positioned between the rail 130 and arm 124, is joined with the arm 124 through a pin 122 with play.
By providing this play, the accidental deformation or the manufacturing error in size of the vehicle parts is absorbed. Thus, the deflection absorbing mechanism does not transmit the load caused by the deformation to the weight sensor 120.
The floor carpet 300 composed of a cushion layer 320 and a surface layer 330 is laid on the floor panel 200. The floor carpet 300, as shown in FIG. 8, is molded into the almost same shape as the floor panel 200.
An installation area 301, onto which a driver's seat is provided, and an installation area 302, onto which a passenger seat is provided, are hollowed than the remainder of the floor carpet 300. The installation area 301 is surrounded by a front-wall 303, a rear-wall 305, an outside-wall 306 and an inside-wall 308. The installation area 302 is surrounded by a front-wall 304, a rear-wall 305, an outside-wall 307 and an inside-wall 309.
A part of the top of a floor-tunnel 210 of the floor panel 200 is covered with a tunnel cover 310 provided at the middle of the floor carpet 300. The remainder of the top of the floor-tunnel 210 is not covered with a tunnel cover 310 for allowing the provision of an instrumental center lower cover (not shown) and a center console (not shown). Thus, a notched part 311 is provided between the installation areas 301 and 302. As can be seen from FIG. 8, both side surfaces of the floor-tunnel 210 are covered with the inside walls 308 and 309, respectively.
Respective front-walls 303 and 304, rear-walls 305, outside-walls 307 and 306, and inside-walls 308 and 309 are formed by bending each surrounding areas of the installation areas 301 and 302 so as to surround the bottom (bottom structures) of the seat.
The weight sensor 120 of the seat-weight measurement device 100 is provided at downward position in an outside of respective seat (driver's seat and passenger seat). Here, the term “outside of respective seat” means the position in the vicinity of a vehicle door with respect to the seat.
As can be seen from FIG. 7, therefore, respective weight sensors 120 of the seat (driver s seat and passenger seat) are positioned in the vicinity of outside-wall 306 (or 307) of the floor carpet 300, and the clearance between the weight sensor 120 and the outside wall 306 (or 307) is quite narrow. Here, the width of the clearance is sufficient for inserting only a finger.
The floor carpet 300 is normally attached to the floor panel 200 using a clip (not shown) etc. In this case, if a load due to the occupant's motion in getting on and off the vehicle is applied to the floor carpet 300, the position with respect to the floor panel 200 of the floor carpet 300 may be deviated. That is, the position of the outside wall 306 (307) of floor carpet 300 may be changed to the position shown by dot-dash line (FIG. 7) due to the separation of the floor carpet 300 from the floor panel 200.
In this occasion, if the outside wall 306 (307) of the floor carpet 300 comes in contact with the pin bracket 121 or the head of the pin 122, the motion of the arm 124 may be disturbed. This reduces the accuracy of weight measurement by the weight sensor 120 and may cause a measurement error.
Therefore, the occupant detection apparatus which can prevent the drop of the accuracy in weight measurement that is caused by the floor carpet has been required.